In this context, patent document DE 4000695 C2 describes, for example, a method for producing substantially amorphous poly-alpha-olefins, which are prepared from higher-molecular-weight amorphous poly-alpha-olefins through shear stress above the softening point, in the presence of a radical former, wherein the melt viscosity of the higher-molecular-weight amorphous poly-alpha-olefins is lowered by at least half. The amorphous poly-alpha-olefins produced in this manner can be used in heavy coating masses for carpets, or hot melt adhesives. Peroxides are disclosed as examples of suitable radical formers.
One disadvantage of the above method has been found to be that high safety requirements need to be met, because a variety of radical formers, such as peroxides, exhibit a high hazard potential. Furthermore, as peroxides decay, volatile components are released, which can lead to an undesirable foaming of the degraded polymer in the extruder. In addition, the use of larger amounts of peroxides often leads to inefficiency of the method, because these materials represent a high portion of costs in the total costs of the method.
Beyond peroxides, it is also possible to use oxygen or oxygen-containing gasses in order to degrade polymers in an extruder. Patent document DE 4413093 A1 discloses, for example, a method for producing functionalized low-molecular-weight polymers from waste plastics, in which high-molecular-weight plastics are decomposed under molecular weight reduction at temperatures of 300° C. to 410° C., in the presence of oxygen or oxygen-containing gases.
Due to the difficulty of controlling effective oxygen entry into the polymer melt, the above-mentioned method has problematic reproducibility. Also, in the exclusive use of oxygen or an oxygen-containing gas, even at very high temperatures, it is not always possible to make the degradation process so effective that polymers with low viscosities are obtained.